Automatically controlled antenna tuning and loading system



7, 1954 M. T. LUDVIGSON ETAL 3,117,279

AUTOMATICALLY CONTROLLED ANTENNA TUNING AND LOADING SYSTEM Filed June 4, 1962 2 Sheets-Sheet 2 RF w PHASE SOURCE UIbCRIMINATOR INVENTORS MERE/LL 7. LUDV/GSON V/RG/L 1.. NE WHOUSE ATTORNEYS United States Patent 3,117,279 AUTGMATICALLY CONTRGLLED ANTENNA TUNING AND LOADING SYSTEM Merrill '1. Ludvigson, Cedar Rapids, and Virgil L. Newhouse, Marion, Iowa, assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed June 4, 1962, Ser. No. 199,?87 11 Claims. (Cl. 325-174) This invention relates, generally, to a control circuit for tuning an antenna coupler and, more specifically, to control means for insuring that tuning of the coupler is completed properly.

It is necessary in many modern electronic equipments to provide rather complex antenna coupling means. Such coupling means is necessary in order to maintain the input impedance of the antenna assembly substantially the same as the output impedance of the transmitter; thus providing optimum conditions for transmission of the signal.

Tuning of the antenna coupling means, generally speaking, is accomplished in the following manner. A load discriminator is provided to detect any deviation of the absolute magnitude of the impedance presented by the antenna assembly (which includes the coupling means) from a desired magnitude. Also provided is a phase discriminator which functions to detect any difference in phase angle between the voltage and the current of the RF signal being supplied to the antenna assembly. Such deviation of the absolute impedance magnitude from a desired magnitude and such difference in phase angle between the voltage and the current of the RF signal represents mismatching of the antenna assembly input impedance and the output impedance of the RF section, either in magnitude or in phase. Such mismatching is to be corrected by the tuning of the antenna coupling means. By employing appropriate servo motor responsive to the output signals of the loading discriminator and the phasing discriminator, the impedance of the coupling means is adjusted so that its absolute magnitude will be equal to the absolute magnitude of the output impedance of the RF section and its reactive component will be the same as the reactive component of the RF section. Actually, in most cases the impedance is purely resistive in nature so that reactive components will not be present when tuning is completed.

Generally speaking, the tuning is initiated by an operator manually keying the transmitter into the antenna assembly circuit through the phasing and loading discriminators. A threshold detecting circuit functions to indicate the presence of an error signal from either the phasing or loading discriminator, and is designed to maintain energization of a control circuit so that the transmitter will remain keyed to the antenna circuit. For a more detailed description of a prior art antenna coupler control circuit, reference is made to US. Patent 2,921,273 issued January 12, 1960, to Samuel L. Broadhead, Jr. et a1. and entitled Automatic Antenna Coupler and which is incorporated herein as a part of this specification.

Certain difficulties are present with the foregoing system, however. For example, when the operator first connects the RF section to the antenna assembly, transient currents are likely to occur in the power amplifier in the RF section before the RF section has become warmed up sufiicientiy to produce a valid RF output. Such transient signals are noisy in nature and sometimes produce spurious outputs from the phasing and the loading discriminators which indicate to the threshold detector that tuning is occurring. Furthermore, these spurious output signals from the phasing and the loading discriminators are supplied to the servo amplifiers to cause non-intelligent rotation of the servo motors. It is to be noted that ordinarily there is a time delay built into the system which allows for a warm up period for the RF section. However, the aforementioned transient signals have been found to be capable of deceiving the time delay circuit and associated control circuitry to indicate thereto that tuning has occurred and has been completed successfully at the termination of the transient signals. Control circuit signal means will then function to indicate to the operator that tuning has been completed, whereas actually it has not yet begun.

Another problem associated with the prior art system discussed above can occur in the following manner. After the operator switches the RF section to a new operating frequency it is possible to momentarily lose the RF output signals, mainly owing to large impedance differences between the RF section and the antenna coupling means. The impedance of the coupling means is reflected back into the RF section to cause momentary detuning thereof with resultant loss of the RF signal. Such momentary loss of RF power is also interpreted by the prior art circuit as an indication that tuning has been completed since the error voltage from the phasing discriminator means and the loading discriminator means drop to zero.

An anlysis of the conditions necessary for the proper completion of tuning indicates that two such conditions are necessary. They are, as follows:

(1) The RF signal must be on, i.e., keyed into the antenna coupling circuit.

(2) The error output voltages from the phasing discriminator and the loading discriminator must be zero.

Only when these two conditions are met can the system be certain that tuning has been completed.

It is an object of the present invention to provide a control circuit which will indicate that tuning has been properly completed by simultaneously detecting and indicating the presence of RF signal and the absence of error output signals from both the phasing and the loading discriminators.

A further object is a more reliable circuit for tuning antenna couplers.

A third purpose of the invention is to provide circuit means which will maintain the RF signal keyed into the antenna coupler during tuning of said coupler even though spurious signals might be produced from said RF section, or even though the RF signal might momentarily fail.

A fourth aim of the invention is the improvement of antenna coupling circuits, generally.

In accordance with the invention, there is provided in combination with an RF generating section an antenna coupling circuit having a first portion constructed to be tunable to vary the phase difference between the current and voltage of the RF signal and a second portion constructed to be tunable to vary the absolute magnitude of the impedance of the coupling circuit. Phasing discriminating means and loading discriminating means are pro vided between the RF section and the antenna coupling circuit to detect differences in phase and load magnitude characteristics of the RF signal from desired values to produce error voltages indicative of said differences. Servo motors responsive to said error voltages function to tune the two portions of the coupling means to provide proper phasing and loading of the RF signal. A first threshold detector means is employed to detect an error signal from either the phasing or the loading discriminator and to drive a first relay means when such an error signal is present. Said relay means functions to complete an energizing path for a control circuit which functions to continue the supplying of the RF power to the antenna coupling circuit as long as error signals appear on the output of either the loading discriminator or the phasing discriminator.

A forward power detecting device is employed to indi cate the presence of RF power. Means including a second threshold detector functions to respond to the presence of RF signal to operate a second relay means. When both said first relay and said second relay areenergized there is provided, through the contacts thereof, a completed energizing path for the control circuit which will, in turn, function to maintain the RF section keyed to the antenna coupling circuit.

Other contact means associated with the second relay means is provided to create an alternate energizing path for said control circuit when the RF fails, thus maintaining the RF section keyed to the coupling circuit. The switching circuit, including the first and second relays and their associated contacts is designed so that only when the first relay is de-energized and the second relay is energized is the energizing path for the control circuit opened so that the RF section is disconnected from the coupling circuit, the tuning having been completed at that time.

A feature of the invention is the addition of a third contact means associated with said second relay means which will function to de energize the servo amplifiers when the RF section is oif, thus saving wear on the choppers employedin the servo amplifiers when RF power is not present.

The above-mentioned and other objects and features of the invention will be more clearly understood from the following detailed description thereof when read in conjunction with the drawings in which:

FIG. 1 is a combination block diagram and schematic sketch of the invention; and

FIG. 2 is a schematic diagram of a portion of FIG. 1.

Referring now to FIG. 1, it should be noted at the outset that the control circuit is herein defined as all of the circuit of FIG. 1, except the RF power input source 70, the antenna coupler 85 and the antenna 19. Of the control circuit a large portion thereof is standard circuitry. The portion which has been added to form the principal novelty of the present invention consists of the forward power indicator 16, the threshold detector 13, the relay 29, and its two associated contacts 22 and 23. As will be seen from the following description, it is the specific function of this added structure to assure that the control circuit will not indicate that tuning has been completed until the proper conditions are met. Additionally, the relays 76, 72, 2t and 21 are sometimes herein referred to as switching means, particularly in the claims since obviously means other than relays could perform the particular switching functions that they do perform.

In FIG. 1 power input source 70 can be. coupled to an antenna 19 through a circuit consisting of contact 75, forward power indicator means 10, load discriminator 11, phase discriminator 12, and antenna coupling means 85.

The functions of the load discriminator 11 and the phase discriminator 12 are, respectively, to detect a variation of the absolute magnitude of the load presented by the antenna coupler 85 from a desired magnitude and to detect the phase difference between the current and the voltage of the RF signal supplied to the antenna coupler means 85. It is to be noted that it is usually desirable that the load impedance of the system be purely resistive in nature so that the phase angle between the current and the voltage supplied to the phase discriminator 12 should be zero.

Servo motor amplifiers 14 and 15 amplify and convert to a more convenient alternating current voltage the direct current error voltages generated by the phase discriminator 12 and the load discriminator 11 when either the phase or the load impedance deviates from a desired value. Servo motors 17 and 18 are driven, respectively, by the output signals of amplifiers 14 and 15 and function, respectively, to tune variable capacitors 27 and 28 to produce proper phasing and loading characteristics of the coupling circuit 85.

By means of or circuit 101 the threshold detector circuit 16 will function to detect an error signal either from A the servo motor amplifier 14 or from the servo motor amplifier 15. More specifically, if an error signal should be present at the output terminals of either amplifier 14 or amplifier 15, the threshold detector will produce a DC. output signal to energize relay 21 and thus close the contact 24. A second threshold detector 13 functions to respond to a signal above a given threshold from the forward power indicator 10 to energize the relay and close the contact 22. The forward power indicator 10 functions merely to produce a DC. output signal indicating that the RF signal is on.

It is important to note that the control circuit 82 will function to maintain the RF signal on as long as a ground potential is supplied to the input control lead once the holding contact of relay 72 has been closed. Such holding contact is closed initially by the operators depressing of the starter button 81 which operates relay 72 and closes the holding contact 86. Operation of relay '72 will also close contact 75 to key the RF signal (block into the antenna coupler through blocks 10, 11, and 12.

An examination of FIG. 1 will show that ground potential will remain on the lead 30 until two conditions exist simultaneously. These conditions are, firstly, that the RF power be keyed into the circuit to produce energization of relay 20 and, secondly, that the error output voltages from both the discriminators 11 and 12 be of zero magnitude to produce a de-energization of relay 21. Under such conditions the contact 22 will be closed and the contact 24 will be open so that the ground potential 102 will be isolated from the lead 39. If the relay 20 is deenergized due to loss of RF, ground potential will be supplied to the lead 30 through the closed contact 23.- If both relay and relay 21 are energized, ground potential will be supplied to the lead 30 through the closed contacts 22 and 24 to maintain energization of the relay 72.

Relay 78 of control circuit 82, which will become energized when contact 73 of relay 72 closes, functions to prepare a closed circuit for the lamp 88, which closed circuit will be completed when relay 72 becomes deenergized to close contact 8'7.

Servo amplifiers 14 and 15 each contain a chopper (not specifically shown in the drawings) and are thereby enabled to respond to D.C. signals from the discriminators 11 and 12 to produce an A.C. signal whose phase is dependent upon the polarity of the DC. input. The phases of the AC. output signal of amplifiers 14 and 15 determine the direction of rotation of the servo motors 17 and 18, respectively.

The choppers are actuated by the 400 c.p.s. signal source 69. It is to be noted that it is necessary to have the choppers operating only when a D0. error is supplied thereto. Consequently, since D.C. errors can occur only when the RF input source is keyed into the circuit, the 400 c.p.s. source 69 is supplied to the choppers through the contact 89 of relay 20, thus causing disconnection of the 400 c.p.s. source 69 from the choppers when the RF signal is not present.

A discussion of the operation of the circuit of FIG. 1 will now follow. Assume that the relays 72, 76, 20 and 21 are all de-energized. Under these conditions the RF power input source 76 is disconnected from the circuit and no error signals are present in the circuit. Assume, further, that the operator has selected an RF signal frequency which is diiferent from the frequency to which the antenna coupling means 85 is tuned. Consequently, tuning of the coupling circuit 85 will be required. To initiate tuning, the operator depresses the starter key 81 which supplies ground potential to sloW-to-release relay 72 (shown in its normally open position), thus closing contacts 75, 73, holding contact 86, and opening contact 87.

Closure of contact will connect the RF signal into the circuit which, since the antenna coupling circuit 85 is mistuned therewith, will produce error output voltages on the output leads 56 and 89 of discriminators 11 and 12, respectively. Servo amplifiers 14 and 15 will then function to cause the servo motors 17 and 18 to begin rotating in the proper direction to correct for loading and phase deviations. The threshold detector 16 will respond to a 400 c.p.s. output signal from either or both of the servo amplifiers 14 and 15 to cause energization of relay 21, thus closing its armature upon contact 24. An output signal will also appear on the output terminal 55 of the forward power indicator 10 which will be detected by the threshold detector 13 to cause energization of relay with a subsequent making of the contact 22. A ground return path can now be traced from ground potential 102, through contact 22, contact 24, lead 39, holding contact 86 of relay 72, the winding of relay 72 to the positive battery 79, thus maintaining the relay 72 in an operative condition.

The closure of contact 73 functions to energize slowto-release relay 76 in a circuit extending from the grounded lead 30 through contact 73, the winding of relay 76 to positive battery source 79. When relay 76 is energized, contact 77 and holding contact 78 will be closed. Ground potential will be supplied to the winding of relay 76 through holding contact 78 and the upper contacts of manual key 81 as soon as the operator releases the key. Closure of contact 77 functions to prepare a circuit for the lighting of lamp 88 when relay 72 later becomes de-energized upon completion of tuning, as will be discussed hereinafter. (Since relay 72 is now energized contact 87 is open, thus preventing energization of lamp S8.)

If, during the tuning of the antenna coupling circuit, the RF power should be temporarily lost due to large impedance mismatch between the RF source 70 and the coupling circuit 35, for example, the output signal of the forward power indicator 19 will drop to zero, thus causing de-energization of the relay 20. Also, the output error signal of the discriminators 11 and 12 will drop to zero, causing de-energization of relay 21. When the relay 20 is de-energized the armature thereof will make with contact 23, thus providing a continued ground potential to the winding of slow-to-release relay 72, and thereby maintaining said relay 72 in an energized condition.

Once energized, the only conditions under which the relay 72 can become de-energized, and thus disconnect the RF power supply from the circuit, are when relay 20 is energized and relay 21 is de-energized. Only under these conditions is the ground return path removed from the winding of relay 72. Also, it is to be noted that under these conditions the RF voltage must be in an on condition to cause energization to relay 2%, and the error output signals from discriminators 11 and 12 must be zero.

When tunin is completed and ground potential is removed from the lead 38 to de-energize the relay 72, the contacts 75, 73, and 86 will open and the contact 87 will close. Since the contact 78 of relay 76 is already closed, ground potential will be supplied to the lamp 88, thus causing energization of lamp 83 and indicating to the operator that tuning has been completed. It is to be understood that any device may be substituted for the lamp 88, which device may be employed to indicate to other equipment that tuning has been completed. Pressing the starter key 81 to start a new cycle will release relay 76.

Referring now to FIG. 2, there is shown a schematic diagram of a portion of FIG. 1. Specifically, FIG. 2 shows a schematic diagram of the block 71 of FIG. 1 which contains the forward power indicator 1% and the load discriminator 11. It should, perhaps, be noted that while the forward power indicator 1G and the load discriminator 11 of FIG. 1 are shown as separate blocks, actually the two circuits are very closely inter-related and cannot readily be separated into two separate blocks in actual construction, as will be seen from the following discussion.

In FIG. 2, the blocks and 92 and the choke 51 show the schematic diagram for the load discriminator 11. The circuitry within the block 91 represents the additional circuitry which in =co-operation with the blocks 90 and 92, functions to produce the indication of forward power.

The blocks 9% and 92, which represent the diagram of the load discriminator, will be discussed first. The circuit is fairly standard and functions, generally, to produce a DO voltage whose magnitude is proportional to the vector difierence of the instantaneous current and voltage appearing on the main line 56. Such vector difference will produce an indication of the absolute magnitude of the impedance load presented to the line 56 by the an tenna coupling circuit. More specifically, the circuit is adjusted so that the DC. signals derived from the instantaneous voltage and the instantaneous current on the line will be equal (and oppositely poled) when the absolute magnitude of the load is of the proper value. Therefore, when the difference between the said two D.C. voltages is zero, the absolute magnitude of the impedance is proper. It is to be noted that no correction for phase is made by the circuit just described. 1

Referring to block 90 in more detail, the current in the line 56 is detected by winding 40 which is loosely coupled to said line 56. The current induced in secondary winding 40 is detected by diode 42 and with a resultant DC voltage produced across the resistor 68. Capacitor 94 performs a return path for the AC. component of the detected signal. Thus, the magnitude of the voltage appearing across the resistor 68 is proportional to the magnitude of the instantaneous current in the line 56.

The voltage appearing on the line 56 is detected by a voltage divider comprised of capacitors 48 and 49. A detection circuit comprising detector 54 resistor 52, and capacitor 98 is connected across the capacitor 49 and functions to detect the AC. voltage thereacross to produce a resultant DC. voltage across the resistor 52. The capacitor 98 actually for-ms a return path for the AC. components of the detected signal, leaving a filtered D.C. across the resistor 52. Choke 100 forms a DC. return path for the diode 50.

It is to be noted that the diodes 42 and 50 are poled in such a manner that the DC. voltages appearing across resistors 68 and 52 are opposed to each other. Thus, if the voltages across resistors 68 and 52 are equal, zero voltage will appear on the output lead 56 which leads to the servo amplifier 15 of FIG. 1.

For purposes of illustrating further the operation of the circuit of FIG. 2, assume that the impedance of the coupling circuit 85 of FIG. 1 is too large. Thus, the current in the line 56 will be smaller than desired with the result that a smaller DC. voltage will appear across the resistor 68 than will appear across the resistor 52. The resultant output DC. voltage appearing on line 56 will then be a negative voltage which will drive the servo motor 18 in the proper direction to decrease the absolute impedance of the antenna coupler. On the other hand, it the resistance of the antenna system were too small, the current in line 56 would be too large so that the DC. voltage appearing across resistor 68 would be larger than that appearing across resistor 52. Thus, the resulting DC. voltage appearing on line 56 would be positive in nature and would cause the servo motor 18 to rotate in the opposite direction to make the necessary impedance correct-ion. The choke 51 is provided to keep RF currents out of the circuit, including resistors 68 and 52.

Referring noW to the circuit within the dotted rectangle 91, it is to be noted that the general purpose of such circuit is to produce a DC. voltage output on lead 55 which indicates the presence of forward power in the line 56. This is accomplished by adding the current and voltage vectors appearing in line 56 and then detecting the resultant vector. More exactly, the voltage vector appearing at point 58 (representing the current in line 56) is added to the voltage vector appearing at point 97 (representing the voltage in line 56) across the circuit within the rectangular block 91. The diode 43 functions to detect the resultant voltage vector appearing thereacross to produce a DC output on the lead 55. It should be noted specifically that either the voltage vector representing the current in the line 56 or the voltage vector representing the voltage in the line must be reversed by 180 in order to properly represent forward power. In other words, if the current and voltage were actually in phase in line 56, thus representing a purely resistive load, the application of a current-representing vector to the anode of diode 43 and the application of a voltage-representing vector exactly in phase with the current-representing vector to the cathode of the diode 43 would result in almost no current fiow through the diode 43. Either the current-representing vector or the voltage-representing vector must be reversed 18G to represent the maximum flow of power through line 56. Such reversal of one of the vectors is accomplished simply by connecting the anode of diode 43 through capacitor to the proper terminal of secondary winding 49.

Capacitors 44 and 45 are D.C. isolating capacitors and serve to keep the DC. voltages existing within the blocks 90 and 92 from the circuit of block 91. The chokes 45 and 47 function to provide a complete DC. path for the DC. current fiowing in the output lead 55.

The detailed schematic circuits of blocks '70, 69, 13, 12, 14, 15, 16, and 101 are standard circuits in the art and will not be described in detail herein. Any good pertinent text may be referred to for specific schematic diagrams of the aforementioned blocks.

It is to be noted that the form of the invention herein shown and described is but a preferred embodiment thereof and that various changes may be made in circuit arrangement such as, for example, the specific design of the control circuit, without departing from the spirit and the scope of the invention.

We claim:

1. In combination with first load means including tunable coupling means, a high frequency signal source means, and transmission line means for connecting said signal source means to said first load means, said tunable coupling means capable of being tuned to produce matching of the impedance of said first load means with the impedance of said signal source means, tuning control circuit means comprising power indicator means and discriminator means, coupled to the output of said signal source to detect, respectively, the presence of forward power from the signal source, and deviation of predetermined characteristics of the impedance presented to said signal means from predetermined values, servo means responsive to the output signals of said discriminator means to tune said tunable coupling means, first switching means constructed, when energized, to connect said signal source to said transmission line means, and initiating means for initiating energization of said first switching means, said first switching means comprising an input control lead and constructed to respond to a predetermined reference potential supplied thereto to maintain energization thereof, after being initially energized by said initiatingmeans, means including second switching means constructed to respond to the output signals from said power indicator and said discriminator means to complete a circuit path for supplying said reference potential to said input control lead when there is an output signal from said discriminator means, said second switching means further constructed to respond to an output signal from said power detector and no output signals from said discriminator means to disconnect said reference potential from said input control lead.

2. Tuning control circuit means in accordance with claim 1, in which said initiating means comprises a manually operable contact means constructed, when actuated, to ergize said first switching means.

3. Tuning control circuit means in accordance with claim 2 comprising indicator means for indicating that tuning has been completed, third switching means responsive to energization of said first switching means to prepare an energizing circuit for said indicating means, said first switching means being constructed when de-energized to complete said energizing circuit for said indicating means to cause said indicating means to indicate that tuning has been completed.

4. Tuning control circuit means in accordance with claim 1 in which said second switching means comprises third and fourth switching means each constructed to inde pendently open said circuit path in a series manner be tween said reference potential and said input control lead means, said third switching means further constructed. to respond to the output signal from said discriminator means to complete a portion of said circuit path when said fourth switching means is actuated in response to an output signal from said power indicator means, said fourth switching means being further constructed to have two conditions and to assure said first condition in response to an output signal from said power indicator means to supply said reference potential to said circuit path and when in said second condition to supply said reference potential directly to said input control means.

5. In combination with first load means including tunable coupling means, a high frequency signal source means, and transmission line means for connecting said signal source means to said first iload means, said tunable coupling means capable of being tuned to produce matching of the impedance of said first load means with the impedance of said signal source means, tuning control circuit means comprising forward power indicator means, load discriminator means, and phase discriminator means coupled to the output of said signal source to detect, re-

spectively, the presence of forward power from the signal source, and deviation of the absolute magnitude of the impedance presented to said signal source means from a predetermined value, anddeviation of the phase between the current and voltage vectors of the output signal of said signal source means, servo means responsive to the output signals of said load discriminator means and said phase discriminator means to tune said tunable coupling means, first switching means constructed, when energized, to connect said signal source to said transmission line means, initiating means for initiating energization of said first switching means, said first switching means comprising an input control lead and responsive to a predetermined reference potential supplied thereto to maintain energization thereof after being initially energized by said initiating means, means including second switching means constructed to respond to the output signals from said forward power indicator and said load and phase discriminator means to supply said reference potential to said input control lead when there is an output signal from either of said load discriminator means and said phase discriminator means, said second switching means further constructed to respond to an output signal from said forward power indicator means and to no output signals tfrom said load and phase discriminators to disconnect said reference potential from said input control lead.

6. Tuning control circuit means in accordance with claim 5, in which said initiating means comprises a manually operable second switching means constructed, when actuated, to energize said first switching means.

7. Tuning control circuit means in accordance with claim 6 comprising indicator means for indicating that tuning has been completed, third switching means responsive to energization of said first switching means to prepare an energizing circuit for said indicating means, said first switching means being constructed when de-energized to complete said energizing circuit for said indicating means to cause said indicating means to indicate that tuning has been completed.

8. Tuning control circuit means in accordance with claim in which said second switching means comprises third and fourth switching means each constructed to independently open said circuit path in a series manner between said reference potential and said input control lead means, said third switching means constructed to respond to the output signal from said discriminator means to complete a portion of said circuit path when said fourth switching means is actuated in response to an output signal from said power indicator means, said fourth switching means being further constructed to have two conditions and to assume said first condition in response to an output signal from said power indicator means to supply said reference potential to said circuit path and when in said second condition to supply said reference potential directly to said input control means.

9. In combination with a first control circuit means for controlling the tuning of the loading and phase characteristics of tunable coupling means constructed to couple the output transmission line of a signal source to a load, second control circuit means constructed to maintain operation of said first control circuit until tuning has been completed, said first control circuit means comprising discriminator means constructed to produce an output signal in response to deviation of the impedance of said tunable coupling means from a desired impedance, servo means constructed to respond to the output signal of said discriminator means to tune the impedance of said tunable coupling means to the value of said desired impedance, first switching means constructed when energized to connect said signal source to said output transmission line, said first switching means having control input lead means connected thereto and, once energized, constructed to maintain energization when a predetermined reference potential is supplied to said control input lead means, and initiating means for initially energizing said first switching means, and first signal detecting means including second switching means responsive to an output signal of said discriminator means to prepare a path for supplying said reference potential to said control input lead means, said second control circuit means comprising power indicator means constructed to produce an output signal in response to forward power in said transmission line, second signal detecting means including third switch ing means constructed to have two conditions and to respond to an output signal from said power indicator means to complete the path through and including said second switching means for supplying said reference potential to said control input lead means, said third switching means further constructed to respond to an absence of signals from said forward power indicator means to assume its second state and to supply said reference po tential directly to said control input lead.

10. Control circuit means in accordance with claim 9, in which said initiating means comprises a manually operable contact means and is constructed to energize said first switching means when actuated.

11. Control circuit means in accordance with claim 10, comprising indicating means for indicating that tuning has been completed, fourth switching means responsive to energization of said first switching means to prepare an energizing circuit for said indicating means, said first switching means being constructed when de-energized to complete said energizing circuit for said indicating means to cause said indicating means to indicate that tuning has been completed.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,117,279 January 7, 1964 Merrill T. Ludvigson et all,

It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 21, for "assure" read assume Signed and sealed this 2nd day of June 1964,,

(SEAL) Attest:

ERNEST W; SWIDER EDWARD J. BRENNER Avllesting Officer Commissioner of Patents 

1. IN COMBINATION WITH FIRST LOAD MEANS INCLUDING TUNABLE COUPLING MEANS, A HIGH FREQUENCY SIGNAL SOURCE MEANS, AND TRANSMISSION LINE MEANS FOR CONNECTING SAID SIGNAL SOURCE MEANS TO SAID FIRST LOAD MEANS, SAID TUNABLE COUPLING MEANS CAPABLE OF BEING TUNED TO PRODUCE MATCHING OF THE IMPEDANCE OF SAID FIRST LOAD MEANS WITH THE IMPEDANCE OF SAID SIGNAL SOURCE MEANS, TUNING CONTROL CIRCUIT MEANS COMPRISING POWER INDICATOR MEANS AND DISCRIMINATOR MEANS, COUPLED TO THE OUTPUT OF SAID SIGNAL SOURCE TO DETECT, RESPECTIVELY, THE PRESENCE OF FORWARD POWER FROM THE SIGNAL SOURCE, AND DEVIATION OF PREDETERMINED CHARACTERISTICS OF THE IMPEDANCE PRESENTED TO SAID SIGNAL MEANS FROM PREDETERMINED VALUES, SERVO MEANS RESPONSIVE TO THE OUTPUT SIGNALS OF SAID DISCRIMINATOR MEANS TO TUNE SAID TUNABLE COUPLING MEANS, FIRST SWITCHING MEANS CONSTRUCTED, WHEN ENERGIZED, TO CONNECT SAID SIGNAL SOURCE TO SAID TRANSMISSION LINE MEANS, AND INITIATING MEANS FOR INITIATING ENERGIZATION OF SAID FIRST SWITCHING MEANS, SAID FIRST SWITCHING MEANS COMPRISING AN INPUT CONTROL LEAD AND CONSTRUCTED TO RESPOND TO A PREDETERMINED REFERENCE POTENTIAL SUPPLIED THERETO TO MAINTAIN ENERGIZATION THEREOF, AFTER BEING INITIALLY ENERGIZED BY SAID INITIATING MEANS, MEANS INCLUDING SECOND SWITCHING MEANS CONSTRUCTED TO RESPOND TO THE OUTPUT SIGNALS FROM SAID POWER INDICATOR AND SAID DISCRIMINATOR MEANS TO COMPLETE A CIRCUIT PATH FOR SUPPLYING SAID REFERENCE POTENTIAL TO SAID INPUT CONTROL LEAD WHEN THERE IS AN OUTPUT SIGNAL FROM SAID DISCRIMINATOR MEANS, SAID SECOND SWITCHING MEANS FURTHER CONSTRUCTED TO RESPOND TO AN OUTPUT SIGNAL FROM SAID POWER DETECTOR AND NO OUTPUT SIGNALS FROM SAID DISCRIMINATOR MEANS TO DISCONNECT SAID REFERENCE POTENTIAL FROM SAID INPUT CONTROL LEAD. 